Thermoplastic polyester resins such as polyalkylene terephthalate resins have excellent mechanical and electrical properties, as well as desirable physical and chemical characteristics. As a result, polyester resins have been used as engineering plastics in an extensive field of end-use applications including automobiles, electrical and electronic apparatus, and the like.
Although thermoplastic polyester resins can, in and of themselves, be molded into articles, various reinforcements or additives have typically been incorporated in polyester resin compositions (depending upon the field of application) so as to obtain improved resin properties, particularly mechanical properties.
It is also well known that the addition of a fibrous reinforcement, such as glass or carbon fibers, imparts desirably high mechanical strength properties and increased rigidity to the thermoplastic polyester resins. However, molded articles formed of thermoplastic polyester resins containing fibrous reinforcement materials tend to distort (warp) and thus cannot be used in environments where close spatial tolerances are required.
The present invention is directed towards solving the distortion problems associated with molded articles formed of fiber-reinforced polyester resins. More particularly, the present invention is directed towards enhancing the distortion resistance of polyester resin compositions containing fibrous reinforcement and/or flaky fillers without damaging the otherwise excellent mechanical properties associated with polyester resins. In this regard, the present invention broadly resides in the use of binder-agglomerated glass granules (to be described below) instead of conventional flaky filler materials in combination with a fibrous reinforcement medium so as to attain polyester resin compositions of decreased distortion when molded.
More specifically, the present invention relates to novel polyester resin compositions including (A) between 20-94% by weight (based on the total composition weight) of thermoplastic polyester resin with (B) between 3 to 65% by weight (based on the total composition weight) of a fibrous reinforcement medium (), and (D) between 3 to 65% by weight (based on the total composition weight) of binder-agglomerated glass granules. The present invention is further characterized by methods to obtain such a composition whereby the above-noted components are mixed together and then melt-blended.